Amyloidosis is a general term that describes a number of diseases characterized by the existence of pathological forms of amyloid proteins, often involving extracellular deposition of protein fibrils, which form numerous “amyloid deposits” or “amyloid plaques,” which may occur in local sites or systematically. These deposits or plaques are composed primarily of a naturally occurring soluble protein or peptide, assembled into extensive insoluble deposits 10-100 μm in diameter in a variety of tissue sites. The deposits are composed of generally lateral aggregates of fibrils that are approximately 10-15 nm in diameter. Amyloid fibrils produce a characteristic apple green birefringence in polarized light, when stained with Congo Red dye. Generally, the fibrillar composition of these deposits is an identifying characteristic for the various forms of amyloid disease.
The peptides or proteins forming the plaque deposits are often produced from a larger precursor protein. More specifically, the pathogenesis of amyloid aggregates such as fibril deposits generally involves proteolytic cleavage of an “abnormal” precursor protein into fragments that aggregate into anti-parallel β pleated sheets.
The fibrillar composition of these deposits is an identifying characteristic for the various forms of amyloid disease. For example, intracerebral and cerebrovascular deposits composed primarily of fibrils of beta amyloid peptide (β-AP) are characteristic of Alzheimer's disease (both familial and sporadic forms), islet amyloid protein peptide (IAPP; amylin) is characteristic of the fibrils in pancreatic islet cell amyloid deposits associated with type II diabetes, and β2-microglobulin is a major component of amyloid deposits which form as a consequence of long term hemodialysis treatment. More recently, prion-associated diseases, such as Creutzfeld-Jacob disease, have also been recognized as amyloid diseases.
In general, primary amyloidoses of the disease are characterized by the presence of “amyloid light chain-type” (AL-type) protein fibrils, so named for the homology of the N-terminal region of the AL fibrils to the variable fragment of immunoglobulin light chain (kappa or lambda).
The various forms of disease have been divided into classes, mostly on the basis of whether the amyloidosis is associated with an underlying systematic illness. Thus, certain disorders are considered to be primary amyloidoses, in which there is no evidence for preexisting or coexisting disease. In secondary or reactive (AA type) amyloidosis characterized by the presence deposition of amyloid protein A (AA) fibrils, there is an underlying or associated chronic inflammatory or infectious disease state.
Heredofamilial amyloidoses may have associated neuropathic, renal, or cardiovascular deposits of the ATTR transthyretin type. Other heredofamilial amyloidoses include other syndromes and may have different amyloid components (e.g., familial Mediterranean fever which is characterized by AA fibrils). Other forms of amyloidosis include local forms, characterized by focal, often tumor-like deposits that occur in isolated organs. Other amyloidoses are associated with aging, and are commonly characterized by plaque formation in the heart or brain. Also common are amyloid deposits associated with long term hemodialysis. These and other forms of amyloid disease are summarized in Table 1 (Tan, S. Y. and Pepys, Histopathology 25:403-414, 1994; Harrison's Handbook of Internal Medicine, 13th Ed., Isselbacher, K. J., et al, eds, McGraw-Hill, San Francisco, 1995) and are described in U.S. Pat. Nos. 6,875,434, 6,890,535, 6,913,745, 6,923,964, and 6,936,246, which are incorporated by reference herein in their entirety.
TABLE 1Classification of Amyloid DiseasesAmyloidProtein/ProteinPeptidePrecursorProtein VariantsClinicalAASerum Amyloid AReactive (secondary)Protein (ApoSSA)Amyloidosis:Familial Mediterranean feverFamilial amyloidnephropathy with urticariaand deafness (Muckle-Wells syndrome)AASerum amyloid AReactive systemicproteinamyloidosis associated(ApoSSA)with systemicinflammatory diseasesALMonoclonalAk, A, (e.g.,Idiopathic (primary)immunoglobulin lightAkIII)Amyloidosis: myeloma orchains (kappa, lambda)macroglobulinemia-associated; systemicamyloidosis associatedwith immunocytedyscrasia; monoclonalgammopathy; occultdyscrasia; local nodularamyloidosis associatedwith chronic inflammatorydiseasesAHIgG (1(γ1))Aγ1Heavy chain amyloidosisassociated with severalimmunocyte dyscrasiasATTRTransthyretin (TTR)At least 30Familial amyloidknown pointpolyneuropathymutations(e.g., Met 30, Portuguese)ATTRTransthyretin (TTR)e.g., Met 111Familial amyloidcardiomyopathy(Danish)ATTRTransthyretin (TTR)Wild-type TTRSystemic senileor Ile 122amyloidosisAapoAIApoAIArg 26Familial amyloidpolyneuropathyAgelGelsolinAsn 187Familial amyloidosis(Finnish)AcysCystatin CGln 68Hereditary cerebralhemorrhage withamyloidosis (Icelandic)AβAmyloid β proteinVarious: GlnAlzheimer's diseaseprecursor (e.g. β-618,Down's syndromeAPP695)Hereditary cerebralhemorrhage amyloidosis(Dutch)Sporadic cerebral amyloidangiopathyInclusion body myositisAB2MBeta2 microglobulinAssociated with chronichemodialysisAcal(Pro) calcitonin(Pro) calcitoninMedullary carcinoma ofthyroidAANFAtrial natriuretic factorFocal Senile Amyloidoses:Isolated atrial amyloidAββ-amyloid precursorBrainproteinSVEPa—Seminal vesiclesAB2MBeta2 microglobulinProstateKeratinPrimary localizedcutaneous amyloid(macular, papular)PrPPrion precursor proteinScrapie proteinSporadic Creutzfeldt-Jacob(33-35 kDa cellular27-30 kDaDiseaseform)Kuru (transmissiblespongiformencephalopathies, priondiseases)AIAPPIslet amyloidIslets of Langerhanspolypeptide (IAPP)Diabetes type II,InsulinomaPeptidee.g., precalcitoninExocrine amyloidosis,hormones,associated withfragmentsAPUDomasaSeminal vesicle exocrine protein
Often, fibrils forming the bulk of an amyloid deposit are derived from one or more primary precursor proteins or peptides, and are usually associated with sulfated glycosaminoglycans. In addition, amyloid deposits may include minor proteins and peptides of various types, along with other components, such as proteoglycans, gangliosides and other sugars, as described in more detail in the sections that follow.
AA fibrils are composed of peptide fragments that range in size but are generally about 8000 daltons (AA peptide or protein) formed by proteolytic cleavage of serum amyloid A protein (SSA), a circulating apolipoprotein which is present in HDL particles and which is synthesized in hepatocytes in response to such cytokines as interleukin (IL)-1 and IL-6, as well as tumor necrosis factor α. See Husby, G. et al. Amyloid 1, 119-137 (1994). The proteolytic cleavage results in the pathologic deposition of an 76-residue N-terminal two thirds of the SAA protein. In humans, the plasma concentration of SAA normally is ˜0.1 mg/ml but can increase over 1,000-fold in response to an inflammatory stimulus. As part of this process, the SAA molecule undergoes proteolysis and the N-terminal cleavage product is deposited systemically as AA fibrils in vital organs, including the liver, spleen, kidneys, and adrenal glands. Deposition is also common in the heart and gastrointestinal tract.
Generally, AA amyloidosis is a manifestation of diseases that provoke a sustained acute phase response. Such diseases include chronic inflammatory disorders, chronic local or systemic microbial infections, and malignant neoplasms. AA amyloid diseases include, but are not limited to inflammatory diseases, such as rheumatoid arthritis, juvenile chronic arthritis, ankylosing spondylitis, psoriasis, psoriatic arthropathy, Reiter's syndrome, Adult Still's disease, Behcet's syndrome, and Crohn's disease. AA deposits are also produced as a result of chronic microbial infections, such as leprosy, tuberculosis, bronchiectasis, decubitus ulcers, chronic pyelonephritis, osteomyelitis, and Whipple's disease. Certain malignant neoplasms can also result in AA fibril amyloid deposits. These include such conditions such as Hodgkin's lymphoma, renal carcinoma, carcinomas of gut, lung and urogenital tract, basal cell carcinoma, and hairy cell leukemia. AA amyloid disease may also result from inherited inflammatory diseases such as Familial Mediterranean Fever. Additionally, AA amyloid disease may result from lymphoproliferative disorders such as Castleman's Disease.
AA Amyloidosis is insidious and progressive. Symptoms are generally presented in later stages of the disease. Frequently the patient is undiagnosed until significant organ damage has occurred. AA fibrils are deposited in vital organs leading to organ dysfunction and subsequently to death. The five year survival rate is 45-50%. Median survival after diagnosis is 4-8 years. End stage Renal Disease is the cause of death in 40-60% of cases. See Gillmore J. D. et al., Lancet 358:24-9 (2001).
Currently, there are no approved specific, amyloid-directed treatments for any of the amyloid diseases, including AA Amyloidosis. See Gillmore J. D. et al., Lancet 358:24-9 (2001). Where there is an underlying or associated disease state, therapy directed towards decreasing the production of amyloidogenic protein by treating the underlying disease. For example, current treatment strategy for AA Amyloidosis is to target underlying inflammation, reducing ApoSSA levels to below 10 mg/l. Currently employed therapies include chemotherapy (cholorambucil and MTX), immuno-suppressants (azathioprine), anti-inflammatory drugs (colchicine) and TNF inhibitors. The invention thus fulfills a longstanding need for therapeutic regimes for preventing or ameliorating the effects of AA Amyloidosis.